Thread roll dies

ABSTRACT

The present invention is directed at an improved thread rolling die, comprising flat parallel longitudinal top and bottom edges, flat tapered die ends, and a vertical face that is used in producing the thread. Formed on the face is a series of parallel ridges which include a plurality of flanks positioned at a pre-determined angle. The ridges are complementary to the thread to be produced and are at an acute angle relative to the top and bottom edges. The ridges are configured for producing a thread helix when a blank is rolled between a set of dies. The thread roll dies have flat narrow surfaces at an angle of less than 60 degrees from the vertical face of the die, rather than being perpendicular to the longitudinal axes of the ridges. The top edge of the die leading to the ends of the vertical face of the die and leading away from the top surface of the die at a 60 degree angle. The ends of the die are positioned approximately 30 degrees from the perpendicular position to create smoother threads.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This patent application claims the benefit of U.S. Provisional Application No. 60/296,626 filed Jun. 7, 2001, entitled Thread Roll Dies, Low Strain Rate, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to improvements in thread roll dies and more particularly to improvements in the design of roll dies that reduces scrap and produces better fasteners.

[0003] The function of placing threads on a bolt by the use of thread rolling dies is old in the art. However, there have been important improvements in the methodology and processes over the years, particularly in the area of the thread transition zone. The thread transition zone, also known as a runout area, is the area defined by the distance from the last full thread to the beginning of the shank or grip section of the bolt. In normal bolt thread rolling practice, this length of thread dissipation is approximately 2 thread pitches long. However, in aerospace applications, the reduction in transition zone has proved very useful. Reduced transition zone is desirable because it saves weight, shortens the thread transition zone by reducing the overall thread length, and does not deteriorate the performance. U.S. Pat. Nos. 4,735,537, 4,842,466, 4,915,559, and 5,039,265 and other similar designs have been successful in reducing the thread transition runout area to well below 1 thread pitch length.

[0004] However, the abrupt change in cross-sectional area to improve the thread transition zone has caused significant difficulties during the thread rolling process. This has especially became apparent when high strength and malleable materials such as titanium and other high strength corrosion resistant steels are used. These problems have manifested themselves by increasing frequency of laps, seams and shear bursts in the root of the thread and discontinuities.

[0005] Therefore, it is desirable to have thread roll dies that incorporate the features of shortened thread transition length with a minimal occurrence of any unacceptable thread discrepancies. It is also desirable to have these dies produce less stress and strain rate in the thread transition area of the bolt.

BRIEF SUMMARY OF THE INVENTION

[0006] The present invention is directed at an improved thread rolling die, comprising a flat parallel longitudinal top edge and bottom edges, flat tapered die ends, and a vertical face that is used in producing the thread. Formed on the face is a series of parallel ridges which include a plurality of flanks positioned at a pre-determined angle. The ridges are complementary to the thread to be produced and are at an acute angle relative to the top and bottom edges. The ridges are configured for producing a thread helix when a blank is rolled between a set of dies.

[0007] The die further comprises a stepped beveled surface which forms a part of the top edge located between the top edge surface of the die and the vertical face; the beveled surface is positioned at a pre-determined angle relative to the top edge surface. The ridges that intersect the stepped beveled surface have ends, that are positioned at a pre-determined angle to the top edge of the die and extend to the stepped beveled surface. The ends blend smoothly into substantially flat surfaces which extend to the top edge surface of the die such that the substantially flat surfaces are positioned at an angle less than 60 degrees from the face of the die. The ends of the improved die lead away at a 60 degree angle from the top edge of the die and are approximately at a 30 degree angle from the top edge of the die.

[0008] The new design embodying the present invention minimizes the negative effects and still continues to reduce the distance of a dimensionally full thread acceptably close to the grip section. This feature is accomplished by changing the fabrication of the thread roll dies by having the flat narrow surfaces at an angle of less than 60 degrees from the vertical face of the die, rather than being perpendicular to the longitudinal axes of the ridges of the prior art. The improvement in the design further includes the top edge of the die leading to the ends of the vertical face of the die and leading away from at a 60 degree angle from the top surface of the die. Additionally, the improvement modifies the ends and angles it approximately 30 degrees from the perpendicular position to create smoother threads.

[0009] In an exemplary embodiment, the stationary die and the moving die are capable of producing less stress and strain in a thread transition area of a fastener and reducing substantial scrap during the manufacture of fasteners with specific dimensions. The design not only reduces stress and strain rate in the thread transition area, but also permits a smooth engagement of a fastener blank between the stationary die and the moving die.

[0010] Other objects, features and advantages of the invention are apparent from the following detailed description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is an enlarged fragmentary perspective view of a prior art movable die depicted in U.S. Pat. No. 4,735,5637;

[0012]FIG. 2 is an exemplary embodiment of an elevational view of a thread rolling stationary die made in accordance with the present invention;

[0013]FIG. 2a is an enlarged perspective view of the thread rolling die;

[0014]FIGS. 2b and 2 c are yet other enlarged perspective views of the thread rolling die depicting various features of the thread rolling die;

[0015]FIG. 3 is a top view of the stationary die shown in FIG. 2;

[0016]FIG. 4 is a side view of the stationary die shown in FIG. 2;

[0017]FIG. 5 is an enlarged fragmentary elevational view of a selected portion 184 of the stationary die shown in FIG. 2;

[0018]FIG. 6 provides other related dimensions for the stationary die for various threads per inch fasteners;

[0019]FIG. 7 is an exemplary embodiment of an elevational view of a thread rolling moving die made in accordance with the present invention;

[0020]FIG. 8 is a plan view of the thread rolling die shown in FIG. 7;

[0021]FIG. 9 is a side view of the thread rolling die shown in FIG. 7;

[0022]FIG. 10 is yet another elevational view of the moving die, respectively;

[0023]FIG. 11 is yet another side view of the moving die;

[0024]FIG. 12 is an enlarged fragmentary view illustrating a typical contour of a corner edge of the moving die; and

[0025]FIG. 13 provides exemplary various dimensions of the stationary die and the moving die and their corresponding face lengths, heights and taper lengths to manufacture the stationary and the moving die.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The prior art disclosed in U.S. Pat. No. 4,735,5637 is incorporated herein by reference. Illustrated in FIG. 1 (identified as FIGS. 5 in U.S. Pat. No. 4,735,5637) is an enlarged fragmentary perspective view of a movable die 46. The movable die 46 is identical in configuration to a stationary die (not shown). The die 46 includes flat parallel longitudinal top and bottom edges 53 and 54, and a vertical face 55 which is used in producing the thread. Formed on the face 55 is a series of parallel ridges 56 which are complementary to the thread to be produced, and therefore generally V-shaped in end elevation. In accordance with standard practice, these ridges include flanks 57 and 58 with a 60 degree included angle between them. The ridges 56 are at an acute angle relative to the top and bottom edges 53 and 54, appropriate for producing a thread helix when a screw blank is rolled between the dies.

[0027] Between the top edge surface 53 of the die and the face 55 is a stepped, beveled surface 59 which forms a part of the upper die edge. This surface is at an angle of 25 degrees relative to the top edge surface 53. Accordingly, the stepped beveled surface 59 is at only a 5 degree differential with respect to the upwardly-facing flanks 57 of the ridges 56 that run out at the beveled surface 59. In practice, the beveled surface 59 is made to blend with the flanks 57 that it intersects. The vertical dimension of the beveled surface 59 should be equal to at least twice the pitch of the thread to be produced in order to assure adequate clearance as the thread is formed.

[0028] The ridges 56 that intersect the stepped beveled surface 59 have relatively abrupt ends 60. As a result, the ridges 56 have their full cross-sectional dimension, symmetrical on either side of their longitudinal axes, at a location close to where they terminate. The only runout of the ridges is provided by the transverse rounded ends 60, which are generally symmetrical about the ridge axes. Preferably, this runout does not exceed one-fourth of the circumference of the thread to be produced at its pitch diameter.

[0029] The rounded ends 60 of the ridges 58 that extend to the surface 59 blend smoothly into flat, narrow surfaces 61 which extend to the top edge 53 surface of the die. This results in the stepped configuration of the beveled surface 59, dividing it into segments, each of which connects to the flank 57 of one of the ridges 56. The narrow surfaces 61 are transverse with respect to the ridges 56, and are perpendicular to the longitudinal axes of the ridges.

[0030] The spacing between the ridge ends 60 is set such that there is an increase in height from one to the next from the die end 62, where the thread rolling begins, to the opposite end 63.

[0031] As illustrated in FIG. 1 above, the thread runout as it exits the top of the die as very abrupt and the termination of the thread in the runout (thread transition zone) area is short and quickly terminated. While this feature is desirable to achieve a minimum distance of a dimensionally full thread as close as possible to the grip or shank section, it does often create undesirable shear bursts, laps, seams and other discontinuities.

[0032]FIGS. 2 and 7 are exemplary embodiments of elevational views of a thread rolling stationary die 90 and a thread rolling moving die 100 respectively made in accordance with the present invention. The dies of this invention are operated as conventional dies, with the one die 90 being moved longitudinally relative to the other die 100. A screw blank is positioned between the dies to produce the screw.

[0033]FIGS. 3 through 6 and 8 through 12 depict various different sectional views of the stationary die 90 and the moving die 100. FIG. 13, in particular, identifies various dimensions of the stationary die 90 and the moving die 100 and their corresponding face lengths, heights and taper lengths to manufacture the stationary and the moving die. The dimensions shown in FIG. 13 are exemplary only, and changes and modifications can be made therein which are within the full intended scope of the invention as herein described and claimed.

[0034] Referring back to FIG. 2, the thread rolling stationary die 90 has a flat parallel longitudinal top edge and bottom edge 102 and 104 respectively, and flat taper die ends 112 and 114 forming a pre-determined angle 116 at both ends of the die. The taper die ends 112 and 114 are tapered relatively at a same angle with reference to a central axis 115 thereby forming a trapezoid shape of the die in conjunction with the vertical face 118 and another vertical parallel face (not shown). In an exemplary embodiment, the pre-determined angle 116 is approximately 10 degree. The die 90 also includes a vertical face 118 that is used in producing the thread. Radii 119 is tangent at “Y” and “L” shown in FIG. 2 to help produce a fastener with a low strain rate. In an exemplary embodiment, dies 90 and 100 are produced from a flat die material having a strength of A.I.S.I. M42. The die material is heat treated and stress relieved.

[0035] As described above, FIG. 2 is an elevational view of the thread rolling stationary die 90. FIG. 3 is a top view and FIG. 4 is a side elevational view of the stationary die 90. Typical dimensions of the stationary die 90 for various different machine sizes are summarized in FIG. 13. For example, for a machine size 10, the stationary die 90 includes the longitudinal top edge 102 having a length (F) of 4.250 inch and the longitudinal bottom edge 104 having a base length (G) of 4.360 inch. The longitudinal top edge 102 and the longitudinal bottom edge 104 are substantially parallel. As shown in FIG. 3, the die 90 also includes the vertical face 118 having a face width (J) of 1.500 inch, which has pre-determined number of ridges 120 complementary to the thread to be produced. The vertical face 118 has a tapered length (K) of approximately 1.700 inch, and another tapered length (L) of 0.600 inch to permit a smooth engagement and disengagement of a fastener between the stationary die 90 and the moving die 100. The die 90 also has the couple of taper ends 112 and 114 having a height (H) of 0.625 inch respectively. FIG. 6 provides other related dimensions for the stationary die 90 which includes various taper depth dimensions identified as “V”, “W”, and “Y” in FIG. 2. FIG. 13 also provides exemplary dimensions 230 for the moving die 100 and the stationary die 90 for machine sizes 20 and 30.

[0036]FIG. 2a is an enlarged perspective view of the thread rolling die 90. As shown in FIG. 2a, formed on the face 118 is a series of parallel ridges 120. The ridges 120 include a plurality of flanks 127 and 128 and are positioned at a pre-determined angle 130. The ridges 120 are complementary to the thread to be produced. The ridges are at an acute angle relative to the top and bottom edges 102 and 104 and further configured for producing a thread helix when a blank is rolled between a set of the stationary die 90, shown in FIG. 2 and the moving die 100, shown in FIG. 7. A stepped beveled surface 144, which forms a part of the upper die edge, is located between the top edge surface 102 of the die and the vertical face 118. The beveled surface 144 is positioned at a pre-determined angle relative to the top edge surface 102. The ridges 127 and 128 that intersect the stepped beveled surface 144 have ends 160, which are positioned at a 60 degree angle to the top edge surface 102 of the die. Additionally, the ends 160 extend to the stepped beveled surface 144 and blend smoothly into the surfaces 162 which extend to the top edge surface 102 of the die such that the surfaces 162 are positioned at an angle less than 60 degrees from the vertical face 118 of the die.

[0037]FIGS. 2b and 2 c are yet other enlarged perspective views of the thread rolling die 90 depicting the stepped beveled surface 144 having ends 160. As shown in FIGS. 2b and 2 c, the ends 162 are positioned at a 60 degree angle to the top of the die 102. Additionally, the ends 160 extend to the stepped beveled surface 144 and blend smoothly into the surfaces 162 which extend to the top edge surface 102 of the die such that the surfaces 162 are positioned at an angle less than 60 degrees from the face 118 of the die. The surfaces 162 are transverse with respect to the ridges 120, being at approximately a 60 degree angle to the longitudinal axes of the ridges 120.

[0038]FIG. 3 is an exemplary embodiment of a top view 170 of the stationary die 100 in accordance with the present invention. Top view 170 displays the vertical face 118 of the die in addition to the flat tapered die ends 112 and 114 with a face width 172 of the die at both the ends. In an exemplary embodiment, a length of notch 174 at a start end of both dies 90 and 100 is of a pre-determined length to ensure smooth engagement and disengagement between the dies and a blank.

[0039]FIG. 4 is an end view 180 of the stationary die 90. The end view 180 shows a height 182 of the stationary die 90. FIG. 5 is an enlarged fragmentary elevational view of a portion 184 of the stationary die 90, shown in FIG. 2. The portion 184 shows an enlarged view of a taper depth 188. The taper depth dimension 164 for the stationary die 90 are the same as the taper depth dimension 165 of the moving die 100 for a given size of the fastener. Exemplary dimensions of the typical tapered depths 164, 165 and a depth 166 in relation to threads per inch 167 produced by various dies are shown in FIG. 6. Additionally, the enlarged view shown in FIG. 5 depicts that the ends 160 extend to the stepped beveled surface 144 and blend smoothly into the surfaces 162 which extend to the top edge surface 102 of the die such that the surfaces 162 are positioned at a pre-determined angle 186. In an exemplary embodiment, the pre-determined angle 186 is an approximate angle of 30 degrees.

[0040]FIG. 7 is an exemplary embodiment of an elevational view of the thread rolling moving die 100 made in accordance with the present invention. FIG. 8 is a top view and FIG. 9 is a side view of the moving die 100. Typical dimensions of the moving die 100 for various different machine sizes are summarized in FIG. 13. For example, for a machine size 10, the moving die 100 includes a longitudinal top edge 202 having a length (A) of 5.000 inches and a longitudinal bottom edge 204 having a base length (B) of 5.110 inches. The longitudinal top edge 202 and the longitudinal bottom edge 204 are substantially parallel. As shown in FIG. 8, the die 100 also includes a vertical face 218 having a face length (D) of 1.500 inches, which has pre-determined number of ridges 220 complementary to the thread to be produced. The vertical face 218 has a tapered length (E) of approximately 4.000 inches to permit a smooth engagement and disengagement of a fastener between the moving die 100 and the stationary die 90. The die 100 also has a couple of taper ends 224 and 226 each having a height (C) of 0.625 inch. FIG. 13 provides exemplary dimensions 230 for the moving die 100 and the stationary die 90 for machine sizes 20 and 30.

[0041]FIGS. 10 and 11 are yet other elevational and side views of the moving die 100. Although, the detail discussions relate to moving die 100, the principles underlying these discussions are equally applicable to stationary die 90. As illustrated in FIG. 7 above, the die 100 has a couple of taper ends 224 and 226. The taper ends 224 and 226 are tapered approximately 10 degrees towards a central axis 240 of the die. The tapered ends 224 and 226 provide smooth engagement and disengagement with the fastener.

[0042]FIG. 12 is an enlarged fragmentary view illustrating a typical contour of a corner edge of the die. FIG. 12 also exemplifies the configuration of the ridges 120. The ridges 120 that intersect the stepped beveled surface 144 (shown in FIG. 2a) have relatively smooth ends 160 which preferably are convexly rounded with compound curvature. As a result, the ridges 120 have their full cross-sectional dimension, symmetrical on either side of their longitudinal axes, at a location close to where they terminate. The only runout of the ridges is provided by the transverse rounded ends 160, which are generally symmetrical about the ridge axes. As illustrated in FIG. 12, the 15 degree angle applies from the beginning of notch and radius along the root radius until it runs out at the edge of the die.

[0043] The new design embodying the present invention and described in FIGS. 2 through 13 minimizes the negative effects and still continues to reduce the distance of a dimensionally full thread acceptably close to the grip section. This feature is accomplished by changing the fabrication of the thread roll dies by having the faces 162 at an angle of less than 60 degrees from the vertical face 118 of the die, rather than being perpendicular (as shown in FIG. 1) to the longitudinal axes of the ridges of the prior art. Additionally, the prior art depicts a radius 60 (shown in FIG. 1) as the thread transitions from the vertical face 118 of the die to the 90 degree angle with sharp corners on the top thread leading to radius 60 and leaving radius 60 on top of the die. The improvement in the design not only radiuses at this point (which is designated as a referenced numeral 160 in FIGS. 2a, 2 b, and 2 c), but also the top edge 102 leading to the ends 160 of the face 118 of the die and leading away at a 60 degree angle from the top surface 102 of the die.

[0044] The prior art further illustrates that the face 60 (shown in FIG. 1) is leading away from the face 55 of die (shown in FIG. 1) and is perpendicular to the flat surface 53 (shown in FIG. 1) of the top of the die. On the other hand, the improvement modifies the surface 160 and angles it approximately 30 degrees from the perpendicular position. This arrangement is exemplified in FIGS. 2, 2a, 2 b, and 2 c above. These differences result in major improvements in reducing scrap and at the same time produce a much better product by avoiding abrupt changes in cross-sectional areas in the manufacturing of dies.

[0045] While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. 

What is claimed is:
 1. A thread rolling die comprising: a flat longitudinal top edge and a parallel flat longitudinal edge; a vertical face having a series of parallel ridges, the ridges include a plurality of flanks positioned at a pre-determined angle, the ridges are positioned at an acute angle relative to the top and bottom edges and are configured for producing a thread helix; and a stepped beveled surface which forms a part of the top edge is located between a top edge surface of the die and the vertical face, the stepped beveled surface is positioned at a pre-determined angle relative to the top edge surface, wherein the ridges intersect the stepped beveled surface and have ends, the ends are positioned at a pre-determined angle to the top edge of the die and blend smoothly into substantially flat surfaces which extend to the top edge surface of the die such that the substantially flat surfaces are positioned at an angle less than 60 degree from the vertical face of the die.
 2. The thread rolling die of claim 1 wherein the ends are leading away at a 60 degree angle from the top edge of the die.
 3. The thread rolling die of claim 1 wherein the ends are approximately at a 30 degree angle from the top edge of the die.
 4. The thread rolling die of claim 1 wherein the ridges are generally V-shaped in end elevation.
 5. The thread rolling die of claim 1 wherein the ridges include a plurality of flanks each separated by a 60 degree angle.
 6. The thread rolling die of claim 1 wherein the stepped beveled surface extends at a 5 degree angle with respect to the upwardly-facing flanks of the ridges that run out at the top edge surface.
 7. The thread rolling die of claim 1 wherein the beveled surface blends with the flanks that it intersects.
 8. The thread rolling die of claim 1 wherein the vertical dimension of the top edge surface is equal to at least twice a pitch of a thread to be produced.
 9. The thread rolling die of claim 1 wherein the ridge ends are convexly rounded, with a compound curvature.
 10. The thread rolling die of claim 1 wherein the stepped beveled surface is positioned at a pre-determined angle of 25 degrees from the top edge of the die.
 11. The thread rolling die of claim 1 wherein the substantially flat surfaces are substantially narrow.
 12. The thread rolling die of claim 1 wherein the substantially flat surfaces are transverse with respect to the ridges and are positioned at an angle less than 60 degree to a longitudinal axes of the ridges.
 13. The thread rolling die of claim 1 wherein the ends are positioned at a pre-determined angle of less than 60 degrees to the top edge of the die.
 14. The thread rolling die of claim 1 wherein the substantially flat surfaces are slightly curved and extend to the top edge surface of the die such that the substantially flat surfaces are positioned at an angle less than 60 degrees from the face of the die
 15. The thread rolling die of claim 1 further having a first end and a second end tapered at approximately 10 degrees towards a central axis of the die.
 16. A moving thread rolling die, said moving die capable of producing less stress and strain in a thread transition area of a fastener and reducing substantial scrap during the manufacture of fasteners, said moving die comprising: a longitudinal top edge having a length (A) and a longitudinal bottom edge having a base length (B), the longitudinal top edge and the longitudinal bottom edge are substantially parallel to each other; a vertical face having a face length (D), which has a pre-determined number of ridges complementary to a thread to be produced, the vertical face having a tapered length (E) to permit a smooth engagement and disengagement of a fastener; and a plurality of taper ends having a height (C).
 17. The thread rolling die of claim 16 wherein the taper ends are tapered at approximately 10 degree towards a central axis of the die.
 18. A stationary thread rolling die, said stationary die capable of producing less stress and strain in a thread transition area of a fastener and reducing substantial scrap during the manufacture of fasteners, said stationary die comprising: a longitudinal top edge having a length (F) and a longitudinal bottom edge having a base length (G), the longitudinal top edge and the longitudinal bottom edge substantially parallel to each other; a vertical face having a face width (J), which has pre-determined number of ridges complementary to the thread to be produced, the vertical face having a tapered length (K) and another tapered length (L) at a pre-determined location to permit a smooth engagement and disengagement of a fastener; and a plurality of taper ends having a height (C).
 19. The thread rolling die of claim 18 wherein the longitudinal top edge has tapered ends, wherein depths of taper at both ends are adjusted to manufacture fasteners with less stress and strain and to reduce the manufacturing scrap. 